Itunes match stopped woking on my Iphone 4s (iOS 6.1.3)

A couple of days ago Itunes Match suddenly stopped to work on my Iphone 4s, but it is still working fine on my other devices.

Basically from one day to another the song disappeared from the Iphone, if try to enable iTunes Match it switches off by itself a couple of seconds later. Very weird.

I went to an Apple store and the only thing they could tell me is to update from iOS6 to iOS7, but I don't want to, since many people with 4s had problems by switching to iOS 7/8.

Has anybody had the same problem?